This invention relates to a method and a system to allow for the preparation of a pressurized water borne paint formulation at the point of retail sale to the ultimate end user.
One of the most significant developments in the field of paints and other protective coatings in the last thirty years has been the rapid growth and widespread acceptance of water-based paints. Since they were first introduced in the later forties as an interior wall finish composed of a water-based styrene-butadiene latex, there has been a great increase in the sale of these paints. The paints are practically odorless during their application and dry rapidly.
Latex wall paints produce a low sheen or gloss finish which has good washability within a short period after application. In cases of scratches, mars or dirt pick-up during this period, it is only necessary to touch up the wall with the original paint. In some cases, however, this has become impracticable because the necessity to save some of the original paint or it becomes inconvenient and time consuming to prepare and clean up the equipment such as brushes and rollers. A convenient solution would be the availability of an aerosol can containing an exact match of the original paint. Unfortunately, however, prepackaged water based aerosols are unstable and have a short shelf life, making them impractical as a retail product. Our invention, as described below, solves this problem.
Since the introduction of the aerosol surface coatings, major steps have been taken to improve the formulation of these materials. Acceptable aerosol dispensed paints must have sufficient mechanical stability to withstand the mechanical shearing forces which aerosol water based paint compositions normally experience as they are dispensed from conventional aerosol containers. Insufficient stability results in mechanical shearing of polymeric components of the composition. Agglomerated bits of the composition can clog the narrow orifices of the aerosol valve outlet and interfere with the even disbursement of paint. Agglomerated bits can also break away for the orifice and be delivered onto the surface of the substrate being painted, thereby marring the paint film thereon.
Mechanical stability of paint formulations is depended in a large measure upon maintaining a solution of the polymer in the aerosolized formulation. Proper mechanical stability and low viscosity have been achieved in solvent based systems employing hydrocarbons, alcohols and other solvents. The volatility of the solvent causes rapid thickening of the paint as the aerosolized composition is dispensed and applied to a substrate. The rapid thickening of the aerosol paint during and after it is dispensed is essential to commercial solvent based paint formulations which must be capable of adhering to vertical surfaces without running. That property of a paint composition is referred to herein as vertical cling.
Although organic solvent based aerosol systems have been developed which have good mechanical stability and vertical cling properties, the solvents employed in such systems (e.g., hydrocarbons or alcohols) are flammable, toxic and environmentally undesirable. Thus, it was deemed desirable to develop a water based paint composition which would possess the degree of mechanical stability necessary for it to be dispensed with a minimum of breakup from a conventional aerosol valve, while at the same time possessing a high degree of vertical cling when the composition is sprayed onto a vertical substrate.
In light of the environmental hazards associated with aerosol propellants such as the fluorocarbon propellants, it is also important to employ a propellant which is environmentally friendly, and possesses a low degree of flammability when used as a propellant for water based concentrate. One such propellant is dimethyl ether, which possesses very low flammability in aqueous systems.
Another problem with solvents in water based paint systems is that over time they begin to react adversely with the paint formulation destroying the desirable properties, such as vertical cling. Accordingly, it is an object of this invention to provide methods and a system whereby a stable aerosol water based paint product can be prepared at the point of retail sale to the person who will ultimately use the paint.
It is another object of this invention to provide an aerosol water based paint composition which employs an environmentally safe and acceptable propellant, while at the same time possessing the key attributes desired in an aerosol dispensed, water based paint, i.e., mechanical stability, the ability to provide a foam-free durable coherent film on the substrate to which the paint is applied, the ability of the composition to cling to vertical surfaces without running, as well as the ability to provide finished paint films having a wide range of gloss. In particular, it is an object of this invention to provide a convenient system whereby a consumer at the retail level can obtain an aerosol can of water borne paint composition that matches a previously purchased paint product.
Yet another object is to provide a system and a method of formulating an aerosol paint composition at the point of retail sale that is stable and ready for immediate use by a consumer. Because the final paint formulation is prepared at the point of retail sale, the contact of the propellant with the water borne paint formulation is significantly minimized, thus avoiding the deleterious degradation of the paint formulation. This results in a stable product with excellent performance characteristics.
Although aerosol water based paints are disclosed by the patent literature (see e.g., Page et al. U.S. Pat. Nos. 4,384,661, 4,265,797, 4,250,253, and 5,071,900; Suk U.S. Pat. Nos. 4,265,797 and 4,450,253; Brouillette et al. U.S. Pat. No. 4,518,734; and Rapaport et al. U.S. Pat. No. 4,482,662), these prior art formulations require that the paint compositions must be specifically formulated to allow them to be aerosolized. However, in our invention, unlike the dimethyl ether propelled compositions of the prior art, we provide a method and system for developing a pressurized can which is capable of accepting water based coatings which are not manufactured specifically to be aerosolized. One advantage of our invention is that it accepts nearly any latex paint without stability problems and prevents agglomeration and gloss loss. It also provides coatings that are environmentally safe, non-flammable and may be cleaned up easily with water.
The present invention provides a method of preparing a aerosol container of water borne paint comprising of a pressurized container having a filling opening and containing a solvent mixture of a volatile propellant, such as dimethyl ether, stabilizers, water and an emulsion. After the selection of a waterborne formulation, for example to match a previously applied paint, it is injected into the pressurized container through the filling opening to form an aerosol container of water borne paint. The present invention provides a method of adding the water borne paint as a last step at the point of retail sale to a mixture of propellant, water, emulsion and stabilizers to allow for flexibility in choice of latex paint used, to ensure stability and to prevent agglomeration.